Prior art parking lock mechanisms for automatic transmissions are well-known. These mechanisms usually include a pretensioned spring to activate the parking lock. The parking lock is typically deactivated by means of a linkage or a hydraulic or pneumatic cylinder. For this purpose, an operating rod of the linkage and/or a connecting rod of the cylinder actuates conjointly with a parking pawl and a parking gear.
From DE 35 37 091 C1, a parking lock is known and includes a parking gear, which is arranged rotationally fixed on the output shaft of the transmission, a pivotable parking pawl, which is movable between an idle and an active position meshing with the parking gear, a lever connected with the manual selector lever, which is connected with an operating rod, via an angled end, with a sliding sleeve opposite the operating rod that may be shifted against the force of an actuating spring. The sliding sleeve is provided with a tapered shoulder to shift the parking pawl from the idle position to the active position, and with a guide for the sliding sleeve in the housing. The end of the operating rod facing the sliding sleeve being upset shaped as a thickened part of the piston, which is shifted in a part of the cylinder of the sliding sleeve.
From U.S. Pat. No. 5,685,406 an arrangement of a parking lock is known, in which a transmission output shaft is connected, in a rotationally fixed manner, with a parking lock wheel, which includes a sort of spline shaft profile on its external diameter. A locking pawl is further provided, which radially meshes by positive locking with the spline shaft profile of the parking lock wheel when the parking lock is activated, thus locking the transmission output shaft. When the parking lock is disengaged, the locking pawl is released from engagement with the parking lock wheel by means of a mechanically operated mechanism, so that the parking lock wheel and/or the transmission output shaft is unlocked and the power train is no longer locked at the output end. The parking lock is likewise disengaged subject to the driver's selection, the driver having to place the selector lever from the parking position into another arbitrary selector lever position.
From DE 199 33 618 A1, by the applicant, a parking lock device for an automatic transmission is further known that comprises a parking lock wheel and a gearing. A locking pawl is engageable with the gearing, as the locking pawl is rotatable in the locked position when bound to a locking device disclosed as a locking cone. The locking cone is shiftably arranged against a spring mechanism on an element connecting with a slotted disk of a selector shaft.
When the parking lock is engaged, the locking pawl is biased into the gearing of the parking lock wheel, by the locking cone, and supported against the guiding plate. With the engaged parking lock, the locking pawl firms up, from the drive wheels, torque engaging the transmission on the output side. This torque is generated, for example, when a vehicle is parked uphill or downhill. In the forward drive direction and the downhill, force, meshing with the vehicle, is introduced to the powertrain on the output side. By locking the transmission output shaft, via the parking lock, the powertrain is held between the drive wheels and the parking lock. When the parking lock is disengaged, the locking pin is shifted in an axial direction, and the locking pawl, held as a consequence of the held power train, is released. In this process, a disadvantageous jolt occurs upon release: The locking pawl hits the guiding plate with its end opposite the parking lock bolt, producing an annoying, loud metallic noise. This noise propagates as an impact sound via the components that are in the force flow path of the locking pawl to the transmission housing and is irradiated outward as a bang, which, when added to the impact, is annoying.
To solve this problem, and/or reduce the noise generated when the parking lock is disengaged, a parking lock device for an automatic transmission is proposed within the scope of DE 102 45 951 A1 by the applicant, in which the parts connected with the transmission housing, i.e. the locking pawl, parking lock bolt and/or guiding plate, are acoustically decoupled by interposing spring and/or damping elements in the force flow.
In DE 102 45 951 A1, a parking lock is taught. A locking pawl, provided for locking a parking lock wheel, is pivotably arranged, via a bearing bolt, in a housing, and is shifted to communicate with a guiding plate, attached to the housing and is further arranged to be parallel to the bearing bolt axis. As a damping measure, it was proposed to acoustically decouple the locking pawl from the guiding plate by a spring arranged between them or a damping link arranged between them. If the locking pawl, previously positively meshing, with the parking lock wheel is pivoted out of this locking position, via an adequate actuating element, the spring and/or the damping element acts to prevent a direct metallic impact of the locking pawl on the guiding plate. Practical experience, however, has shown that when the locking pawl is disengaged from a state of high stress an impact noise still occurs, either by the impact of the spring on an allocated countersurface, locking of the spring, or impact of the damping link on an allocated countersurface, demonstrating that this type of measures is not sufficient to attenuate the release jolt such that, even under extreme vehicle operating conditions, it is not perceived as annoying by the driver.
Another measure for damping the release jolt occurring upon release of the positive locking of the parking lock is proposed in DE 102 45 951 A1. In this, the bearing bolt and/or parking lock bolt, on which the locking pawl of the parking lock is twistably and/or pivotably arranged in the housing, is not directly placed in the housing, but in a rubber sleeve, which is inserted into a corresponding recess and/or bore of the housing.
As a further measure for damping the release jolt occurring upon release of the positive lock of the parking lock is proposed in DE 102 45 951 A1. In this, the upper guiding plate of the parking lock system is acoustically decoupled from the housing by screwing the guiding plate to the housing damping links, such that there is no metallic contact between the guiding plate and housing. From practical experience, however, this type of elasticity has also shown to be insufficient to adequately dampen the noise occurring when the pawl strikes on the guiding plate, when the locking pawl is disengaged from a state of high stress.
From DE 195 35 239 C1, a parking lock is known in which the locking pawl and/or the parking lock wheel are of an elastic ductile design. From practical experience, however, this type of elasticity in the bearing of the locking pawl has a disadvantageous effect. Particularly on precision, when the parking lock is engaged, and also because it is subject to high wear and tear caused, in part, by considerable bearing loads.
Further, within the scope of DE 102 55 714 A1 by the applicant, a proposal is made to prevent the release jolt from occurring upon release of the positive lock of the parking lock, by additionally engaging the output, when the parking lock is activated, with at least connecting one friction locked switching element of the transmission, which is controllably disconnected only when the positive lock of the parking lock is released. However, this procedure disadvantageously requires a complex control device.